Mobile radio telecommunication systems were made up of a cellular structure in which mobile radios move in and out of geographically defined "cells." As it turns out, some mobile radios are more or less mobile than others within the cell structures. Some radios, for example, may be used in more mobile applications and therefore travel across new cell boundaries on the order of every few minutes. A simple mobile radio may also be highly mobile at one time (for example during traditional commuting hours) and less mobile just an hour later.
The mobile radio network is designed to communicate with the mobile radios via broadcast systems within the cell structure. Thus, in an example embodiment, each cell in a geographic area may be serviced by a single base station and each of the base stations in a predefined area may be serviced by a mobile radio switching center. In this example embodiment, the base stations define the cell geographic areas based on the transmission distances and characteristics associated with the respective base station in the cell. Similarly, the mobile radio switching center may define a location area which is geographically defined based on optimal traffic characteristics between the mobile radio switching center and the base stations in the location area.
The mobile radio switching center serves two important functions vis-a-vis any particular mobile radio. First, it keeps a more or less accurate record of the mobile radios location within the cellular structure, in order to be able to find the mobile radio when an incoming call for the mobile radio is received. One method of location updating is for the mobile radio to periodically inform the network of its location. Depending upon the period of location updates, this method may provide good location information for each mobile radio, but does so by burdening the system resources with multiple location update transmissions. Many schemes have been developed to balance and optimize the desirability for increased location knowledge with minimization of the burden of location updating.
Another important process of the mobile radio switching center is paging. The mobile radio switching center sends a page message to a mobile radio whenever an incoming call is received for that mobile radio. This process is well-known and understood in the art. The page message for any particular mobile radio is sent to a location area defined by a number of cells in a neighborhood of cells associated with the last known location of the mobile radio. In this context, the location area is by definition that group of cells (one or more) in which the mobile station may move freely within and still not update the network as to its new location. In essence, the location area becomes the smallest area known to the network where a specific mobile station immediately resides. This grouping of a number of cells into a location area for paging purposes is a known technique.
Another paging technique is described in U.S. Pat. No. 5,289,527, where all cells have a published geographical position and the registration of a mobile radio is valid within a certain radius of that cell position. There, the mobile station will register whenever it moves into a new cell that is greater than the radio distance from the previous cell where it had earlier registered.
In systems where location areas are the smallest known location that a mobile station resides (whether the location area is pre-determined or dynamically determined), the paging message for a particular mobile station is sent on the paging channel to all cells in the location area. Although the page is sent to all cells in the location area, many of the pages on the paging channel will be wasted since the mobile station will only receive one of the messages sent, i.e., the one message sent to the one cell where the mobile station actually resides. That is, the mobile station can only be in one cell at a time and thus will receive one page message from the network even though the network is sending the page message to multiple cells within the location area. All messages sent into cells where the mobile station does not reside for purposes of paging the mobile station represent an unnecessary load on the page control channel.
Of course, the page load can be reduced if the location registration load is increased, meaning that the page load to unnecessary cells will be removed if the system knows the exact location of the mobile station on a cell level based on an increase in location updates. To ensure that pages are focused to areas where a mobile station resides, a location update would have to occur relatively frequently, for example, every time a mobile station entered a new cell. This represents a large location update burden on the system. Balancing the location update cost/burden and the page cost/burden is discussed at length in Location Management Methods For Third-Generation Mobile Systems, IEEE Communications Magazine, August 1997. A balance between the location update mode and the page load is needed, but the prior art teaches that one load (either location update or page) cannot be reduced without the other load being increased.
However, if the mobility of the various radios are taken into account, then the page system can be customized to the particular characteristics of the mobile radio, namely the mobility rate of the mobile radio. Thus, in accordance with an aspect of the present invention, page messages for a mobile radio are issued on either a location area basis or on a cell area basis, depending on the mobility behavior of the mobile station. Various methods of determining mobility of mobile stations are known and the present invention is not limited to any particular such methodology. Depending on the mobility of any particular radio, either the location area level paging is used or a cell level paging is used.
These, as well as other objects and advantages of this invention, will be more completely understood and appreciated by careful study of the following more detailed description of a presently preferred exemplary embodiment of the invention taken in conjunction with the accompanying drawings, of which: